<template>
  <ul class="allist">
    <li class="item" v-for="item of letters" :key="item"
    :ref="item"
     @touchstart="handleTouchStart"
     @touchmove="handleTouchMove"
     @touchend="handleTouchEnd"
      @click="handleLetterClick"
      >{{item}}</li>

  </ul>
</template>
<script>
export default {
  name:'CityAlphabet',
  props:{
    cities:Object
  },
  computed:{
    letters(){
      const letters=[]
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  },
  data(){
    return{
      touchStatus:false
    }
  },
  methods:{
    handleLetterClick(e){
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus=true;
    },
    handleTouchMove(e){
      if(this.touchStatus){
        const startY = this.$refs['A'][0].offsetTop
        const touchY = e.touches[0].clientY -79
        const index = Math.floor((touchY-startY)/20)
        if(index >= 0 && index<this.letters.length)
        this.$emit('change',this.letters[index])
      }
    },
    handleTouchEnd(e){
      this.touchStatus = false
    }
  }
}
</script>
<style scoped>
  .allist{
    display: flex;
    flex-direction: column;
    justify-content: center;
    position: absolute;
    top:1.58rem;
    right: 0;
    bottom: 0;
    width: .4rem;
  }
  .allist .item{
    line-height: .4rem;
    text-align: center;
    color: #00bcd4
  }
</style>


